A comparison has been made of the disease produced in white-tailed deer by the viruses of epizootic haemorrhagic disease and bluetongue. The similar nature of these diseases in deer and of some of the viral properties has been described. Although these two viruses are considered to be distinct, it is possible by employing an unnatural procedure to produce antibody which will demonstrate a minor antigenic component common to both viruses. Biological features that differ between the two viruses have also been noted.